Infection by Gram-negative bacteria such as Pseudomonas aeruginosa, Extended Spectrum β-lactamase producing (ESBL) Enterobacteriaceae, and Acinetobacter baumannii is a major health problem, especially in the case of hospital-acquired infections. In addition, there is an increasing level of resistance to current antibiotic therapies, which severely limits treatment options. For example, in 2002, 33% of Pseudomonas aeruginosa infections from intensive care units were resistant to fluoroquinolones, while resistance to imipenem was 22% (CID 42: 657-68, 2006). In addition, multi-drug resistant (MDR) infections are also increasing; in the case of Pseudomonas aeruginosa, MDR increased from 4% in 1992 to 14% in 2002 (Biochem Pharm 71: 991, 2006).
Gram-negative bacteria are unique in that their outer membrane contains lipopolysaccharide (LPS), which is crucial for maintaining membrane integrity, and is essential for bacterial viability (reviewed in Ann. Rev. Biochem 76: 295-329, 2007). The major lipid component of LPS is Lipid A, and inhibition of Lipid A biosynthesis is lethal to bacteria. Lipid A is synthesized on the cytoplasmic surface of the bacterial inner membrane via a pathway that consists of nine different enzymes. These enzymes are highly conserved in most gram-negative bacteria. LpxC is the enzyme that catalyzes the first committed step in the Lipid A biosynthetic pathway, the removal of the N-acetyl group of UDP-3-O—(R-3-hydroxymyristoyl)-N-acetylglucosamine. LpxC is a Zn2+-dependent enzyme that has no mammalian homologue, making it a good target for the development of novel antibiotics. Several inhibitors of LpxC [UDP-3-O—(R-3-hydroxymyristoyl)-GlcNAc deacetylase] with low nM affinity have been reported (Biochemistry 45: 7940-48, 2006).